This invention relates to displacement measurement systems and sheet feed systems incorporating the same.
Sheet feed systems typically include sheet feed detectors that produce an output having a value that increases with the thickness of sheet layers being fed. Such sheet feed detectors may include mechanical sensors that detect the thickness of the sheet layer, capacitor circuits in which the sheet layer forms the dielectric, and radiation generators and detectors that measure the absorption of photons, electrons, or ions by the sheet layer. The responses of such sheet feed detectors correspond mechanical displacements or electrical signals that may be compared to stored reference values. The result of the comparison typically is a is binary electrical signal that may be used to stop the sheet feed mechanism if the measured thickness is greater than the reference value. A simple mechanical system may use a single micro-switch. An electrical system may use a comparator to drive a relay.
U.S. Pat. No. 4,420,747 has proposed a system for detecting missing or superimposed sheets fed to a sheet processing machine that uses a measuring device to generate a signal that increases with the number of superimposed sheets and an evaluating device that emits an electrical signal when irregularities occur. A pulse transmitter is synchronized to the sheet feed mechanism and operates to emit an initial pulse and a final pulse that are timed to the sheet feed. Electronic storage is reset upon the initial pulse, and operates to integrate values of the measured signal until the final pulse is received. Upon receipt of the final pulse, the stored value is compared to a reference value to detect any irregularities. Preferably, a microcomputer is used for signal processing.
The invention features a displacement measurement system, comprising a support arm, a roller, and an optical encoder. The support arm has a first end and a second end and is configured to turn about a pivot axis on a pivot located closer to the first end than the second end so that displacement of the first end causes a greater corresponding displacement of the second end. The roller is mounted at the first end of the support arm and is configured to rotate about a roller axis substantially parallel to the pivot axis. The optical encoder has at least one component mounted at the second end of the support arm and is configured to generate signals responsive to movement of the second end of the support arm.
The invention also features a sheet feed system, comprising the above-described displacement measurement system, a sheet feed surface, a biasing member, and a controller. The sheet feed surface is disposed adjacent to the roller and is configured to receive a sheet between the sheet feed surface and the roller. The biasing member is coupled to the support arm at a location between the pivot axis and the second end of the support arm and is configured to urge the roller against the sheet feed surface. The controller is configured to sample signals generated by the optical encoder and to compute one or more displacement values based upon one or more sampled signals.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.